1. Field of the Invention
This invention relates to a process for removing photoresist remaining over one or more metal layers after etching of such metal layers. More particularly, this invention relates to a dry process for removing photoresist and also removing or inactivating corrosion-forming etch residues remaining over one or more metal layers after etching of the metal layers.
2. Description of the Related Art
A photoresist mask, which remains over portions of one or more metal layers on an integrated circuit structure after patterning such metal layers through the photoresist mask, has been conventionally removed by dry etch techniques using plasmas of oxygen and fluorocarbon gases. Such dry etch techniques are preferred over wet etch techniques since underlying metals are not attacked, and because the dry etching is sometimes more effective in removal of photoresist residues, particularly when the photoresist has been altered by reactive ion etching, high temperature post bakes, or the like.
However, such dry etch techniques have been found to be less than satisfactory in removing or inactivating certain sidewall etch residues remaining from the previous metal etch (patterning) step. Such metal etch processes conventionally use chlorine-based chemistry, e.g., Cl.sub.2 and BCl.sub.2, which may leave chlorine-containing sidewall residues on the sidewalls of the photoresist mask and underlying metal layer portions after the metal etch.
In this regard, a particular problem exists when etching a titanium-tungsten layer, which may be utilized under an aluminum layer to prevent spiking of the aluminum to an underlying silicon layer. This is because tungsten etch products, such as tungsten chloride, are not as volatile as titanium chloride or aluminum chloride and, therefore, tend to remain on the surfaces of the integrated circuit structure. This apparently occurs even though it is common to use a fluorocarbon metal etch to etch the titanium-tungsten metal layer, after a chlorine etch is used to etch the overlying metal such as aluminum, and such a fluorocarbon etch will remove some of the undesirable chlorine etch products.
If chlorine-containing residues (regardless of their source) in the sidewall residues, remaining after the metal etch step, are not removed or inactivated during the subsequent removal of the photoresist mask, such chlorine-containing residues may cause corrosion of the underlying metal or metals prior to subsequent downstream processing steps which may include washing (solvent-rinse) steps resulting in removal of such chlorine-containing residues.
Since it is known that such subsequent processing steps can result in removal of any chlorine-containing residues remaining in sidewalls from the metal etch step, it has become conventional to judge the effectiveness of the photoresist removal step in also removing or inactivating such chlorine-containing residues based on how much corrosion occurs during a 24 hour period following the photoresist removal step. If no corrosion of the underlying metal or metals occurs within 24 hours after the photoresist removal step, the photoresist removal step is judged to have successfully removed or inactivated a sufficient amount of such corrosion-causing residues, since it is assumed that within 24 hours the integrated circuit structure will have been subjected to subsequent processing which will include at least one subsequent washing step which will remove any remaining chlorine-containing residues.
However, the currently practiced photoresist removal process using O.sub.2 and CF.sub.4, has not succeeded in providing this desired 24 hours of protection from corrosion of the metal or metals by such chlorine-containing residues.
It would, therefore, be desirable to provide an improved process for the removal of photoresist remaining after a metal etch step which would not only remove the photoresist mask, but also remove or inactivate a sufficient amount of any remaining chlorine-containing residues from the metal etching step so that the remaining metal or metals will be passivated or free from corrosion for at least 24 hours after such processing.